Kerr Kelly L, Meinzer Frederick C, McCulloh Katherine A, Woodruff David R, Marias Danielle E
Department of Forest Ecosystems and Society, Oregon State University, Corvallis, OR 97331, USA.
USDA Forest Service, Pacific Northwest Research Station, 3200 SW Jefferson Way, Corvallis, OR 97331, USA
Tree Physiol. 2015 May;35(5):535-48. doi: 10.1093/treephys/tpv034. Epub 2015 May 1.
First-year tree seedlings represent a particularly vulnerable life stage and successful seedling establishment is crucial for forest regeneration. We investigated the extent to which Pinus ponderosa P. & C. Lawson populations from different climate zones exhibit differential expression of functional traits that may facilitate their establishment. Seeds from two populations from sites with contrasting precipitation and temperature regimes east (PIPO dry) and west (PIPO mesic) of the Oregon Cascade mountains were sown in a common garden experiment and grown under two water availability treatments (control and drought). Aboveground biomass accumulation, vegetative phenology, xylem anatomy, plant hydraulic architecture, foliar stable carbon isotope ratios (δ(13)C), gas exchange and leaf water relations characteristics were measured. No treatment or population-related differences in leaf water potential were detected. At the end of the first growing season, aboveground biomass was 74 and 44% greater in PIPO mesic in the control and drought treatments, respectively. By early October, 73% of PIPO dry seedlings had formed dormant buds compared with only 15% of PIPO mesic seedlings. Stem theoretical specific conductivity, calculated from tracheid dimensions and packing density, declined from June through September and was nearly twice as high in PIPO mesic during most of the growing season, consistent with measured values of specific conductivity. Intrinsic water-use efficiency based on δ(13)C values was higher in PIPO dry seedlings for both treatments across all sampling dates. There was a negative relationship between values of δ(13)C and leaf-specific hydraulic conductivity across populations and treatments, consistent with greater stomatal constraints on gas exchange with declining seedling hydraulic capacity. Integrated growing season assimilation and stomatal conductance estimated from foliar δ(13)C values and photosynthetic CO2-response curves were 6 and 28% lower, respectively, in PIPO dry seedlings. Leaf water potential at the turgor loss point was 0.33 MPa more negative in PIPO dry, independent of treatment. Overall, PIPO dry seedlings exhibited more conservative behavior, suggesting reduced growth is traded off for increased resistance to drought and extreme temperatures.
一年生的树苗代表着一个特别脆弱的生命阶段，而成功的幼苗定植对于森林更新至关重要。我们研究了来自不同气候区的西黄松种群在多大程度上表现出可能有助于其定植的功能性状的差异表达。从俄勒冈喀斯喀特山脉以东（PIPO干旱）和以西（PIPO湿润）降水和温度状况截然不同的地点采集的两个种群的种子，在一个共同花园实验中播种，并在两种水分供应处理（对照和干旱）下生长。测量了地上生物量积累、营养物候、木质部解剖结构、植物水力结构、叶片稳定碳同位素比率（δ(13)C）、气体交换和叶片水分关系特征。未检测到与处理或种群相关的叶片水势差异。在第一个生长季节结束时，对照和干旱处理下PIPO湿润种群的地上生物量分别比PIPO干旱种群高74%和44%。到10月初，73%的PIPO干旱幼苗形成了休眠芽，而PIPO湿润幼苗只有15%形成了休眠芽。根据管胞尺寸和堆积密度计算的茎理论比导率从6月到9月下降，在生长季节的大部分时间里，PIPO湿润种群的该值几乎是PIPO干旱种群的两倍，这与比导率的测量值一致。在所有采样日期，两种处理下基于δ(13)C值的内在水分利用效率在PIPO干旱幼苗中都更高。跨种群和处理的δ(13)C值与叶片比水力导率之间存在负相关关系，这与随着幼苗水力能力下降，气孔对气体交换的限制更大相一致。根据叶片δ(13)C值和光合CO2响应曲线估算的生长季节综合同化率和气孔导度，PIPO干旱幼苗分别低6%和28%。无论处理如何，PIPO干旱种群在膨压丧失点的叶片水势比其低0.33MPa。总体而言，PIPO干旱幼苗表现出更保守的行为，这表明生长减少是以增加对干旱和极端温度的抗性为代价的。
